In a context of increasing world energy demand, capture of carbon dioxide for sequestration thereof has become an imperative necessity in order to limit greenhouse gas emissions harmful to the environment.
Oxycombustion is one of the promising methods for energy production involving CO2 capture. Such a method is for example described in patent WO-07,039,687 A. Implementation of this method requires an oxygen production unit that can supply the oxycombustion chamber with oxygen, pure or diluted in a CO2 and/or steam stream.
Another energy production method involving CO2 capture is pre-combustion separation of CO2 by means of IGCC (Integrated Gasification Combined Cycle) type plants, whose principle is described in U.S. Pat. No. 6,824,575. As for oxycombustion, this technology requires an oxygen production unit that can supply a gasification unit with oxygen, pure or diluted in a steam and/or CO2 stream.
Also, the production of synthesis gas (CO+H2) from various carbon-containing raw materials such as coal, petroleum, natural gas, biomass is a key stage in the production of synthesis fuels or hydrogen, which requires oxygen as free of nitrogen as possible so as to avoid diluting the synthesis gas obtained.
In all these cases, it is important to avoid or at least to minimize the presence of nitrogen. On the other hand, it can be advantageous to use a mixture of oxygen and of an inert gas, which can be steam and/or carbon dioxide, easy to separate from oxygen or that can be used as they are, depending on applications.
Currently, the most commonly used technology for production of sufficient amounts of oxygen for this type of methods is air separation by cryogenic distillation, but the energy cost of this technology is high because it requires cooling the air to a very low temperature to allow distillation thereof. The cold oxygen obtained then has to be heated prior to being fed into the oxycombustion chamber or the gasification unit. Furthermore, the production cost of the oxygen obtained considerably increases with the desired purity, and the high energy consumption leads to additional CO2 emissions.
It would therefore be advantageous to have a high-temperature (500° C.-1100° C.) oxygen production method in order to limit the CO2 capture cost.
U.S. Pat. No. 6,059,858, the contents of which are incorporated herein by reference, describes a high-temperature oxygen production technology by selective sorption of the oxygen in the air based on the CAR (Ceramic Autothermal Recovery) process: a ceramic material first reacts selectively with the oxygen in the air, and this oxygen is then desorbed by the material under the action of a decrease in the oxygen partial pressure, created by placing the material under vacuum or by purging it with an inert gas (steam, CO2 or mixture) at constant temperature (partial pressure swing process). The sorption-desorption stages are repeated cyclically, and using several fixed-bed reactors arranged in parallel allows to generate a sufficient oxygen-enriched CO2/steam stream.
A variant of the ceramic regeneration stage consists in raising the temperature at constant pressure (temperature swing process).
Patent FR-2,895,272, the contents of which are incorporated herein by reference, also describes a continuous high-temperature oxygen production method based on the adsorption/desorption properties of perovskite or fluorite type ceramics used in a rotating cylindrical reactor.
The efficiency of these methods first of all depends on the properties of the ceramic material used: oxygen selectivity, oxygen transfer capacity, sorption/desorption kinetics and physico-chemical stability.
These methods require using materials that react reversibly with oxygen according to the temperature and pressure conditions. Several materials meeting these criteria are described in patent applications US-2005/0,176,588, US-2005/0,176,589 and US-2005/0,226,798, among which perovskites, brownmillerites, supraconductive materials of YBaCuO type and mixed oxides of doped ceria and zirconia type. All these materials are known, within a certain temperature range, for their mixed ionic and electronic conduction properties (MIECs, Mixed Ionic Electronic Conductors) and they exhibit, in addition to these conduction properties, a relatively high oxygen sorption capacity. The defects of the various structures (oxygen vacancies, interstitial oxygen sites) allow the materials to react with oxygen at high temperature (they become “laden” with oxygen) and to desorb all or part of this oxygen depending on the temperature and pressure conditions (when the O2 partial pressure PO2 decreases or when temperature T increases). Patent US-2005/0,176,588 also claims the addition of simple metallic oxides (MOn, n=0.5, 1, 1.5, 2, M=Cu, Co, Ni, Bi, Pb, V, Mn, Cr) to the MIECs described above, in order to increase the oxygen transfer capacity of the composite material obtained.